The exemplary embodiment relates generally to sheet registration systems and finds particular application in connection with a controllable registration system for sheet media which is suited to use in a printing system.
Transport systems are widely used for transporting sheet media between and within modules of a printing system, such as between a sheet feeder and a marking module, or on a return path through the marking module to enable duplex (double sided) printing. The transport system may include a combination of rollers, conveyor belts, vacuum-assisted transport units, and the like. To ensure that each sheet arrives at the marking module with an acceptable level of skew and lateral errors, transport systems incorporate registration systems to steer the sheets to achieve correct alignment.
There are demands for new printer designs that can accommodate larger sheet sizes (e.g., to about 66 cm, or greater) without reducing printer speeds. For the registration system, steering long sheets at high speeds is challenging. At high speeds, the time available to perform the registration correction is reduced, which can increase stresses on the sheets. The trailing edge of the sheet may swing out of alignment, creating a ‘tail-wag’ motion of the sheet, when the leading edge of the sheet undergoes correction. This means that sheets may not be correctly registered if their input error is too large, resulting in sheet damage, jams, or sheet slippage, with sheets breaking free of the drive nips, resulting in poor registration.
One type of registration subsystem uses independent drive rolls for correcting skew while lateral correction is effected by a translating (cross process) carriage. This has an advantage of decoupling the lateral and skew correction. However, the use of the translating carriage limits the maximum speed of the printer system due to the limit on the carriage return time that can be achieved, given the mass of the carriage (including motors, rollers and other drive elements).
Another method used to enable registering large sheets is to adjust the positions of preceding modules manually, to try to keep the input error to the marking module low. However, such module alignment procedures impact only the mean input error and are unable to address sheet-to-sheet variations. Thus, even though average input error may be within acceptable bounds, sheet-to-sheet variations can result in misregistration of some of the sheets.
There remains a need for systems and methods for media registration which address these deficiencies and enable improvements in the capability of a printing system to handle faster sheet speeds, larger sheet sizes, and/or larger weight sheets.